JPS59193226A - Denitrification of molten metal in vacuum induction melting furnace - Google Patents

Abstract

PURPOSE:To promote denitrification without obstructing melting work, in a vacuum induction melting furnace, by blowing gas into a molten metal by immersing a lance in said molten metal from the upper part thereof. CONSTITUTION:A base material is melted in a vacuum induction melting furnace 2 or a molten bath is supplied to said furnace 2 from a laddle and maintained at a predetermined temp. while a vacuum tank 1 is evacuated. A lance 3 is immersed in the molten metal in the melting furnace 2 from the upper part of the vacuum tank 1 to blow inert gas such as argon, CO-gas or a gaseous mixture thereof into said molten metal to promote the denitrification of the molten metal under stirring. By this method, the extremely low nitrificaion of the molten metal can be realized and adverse affect is not exerted on furnace refractory. In addition, because the immersion depth of the lance 3 and gas flowing can be arbitrarily set, stirring can be arbitrarily controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for denitrifying molten metal in a vacuum induction melting furnace.

In recent years, as steel has become more sophisticated, there has been an increasing demand for clean steel with extremely low impurities.By reducing nitrogen in the steel as much as possible, it has excellent ultra-deep drawability, especially in thin sheets. It is known.

By the way, the nitrogen solubility C%N''l in molten iron is expressed by the following formula.

[CHN] − to//N outside q However, PN2: Nitrogen partial pressure in the atmosphere LogK −
−”−1,248 tgg/N==Σe4[%1l el: Coefficient of interaction on N of one component in molten iron Therefore, in order to manufacture ultra-low nitrogen steel, the nitrogen partial pressure PN2 in the atmosphere must be It is important to reduce the nitrogen content as much as possible, and one method of melting this extremely low nitrogen steel is to promote denitrification using a vacuum induction melting furnace.

This vacuum induction melting furnace heats and maintains the molten metal by applying an induced current to the molten metal, and at the same time applies an induction stirring force to achieve a low P.
This is aimed at the denitrification effect under N.

However, in this method, the stirring of the molten metal is weak and the denitrification rate is slow, making it difficult to achieve extremely low nitridation even if the treatment is carried out for a long time. For this reason, a method has been proposed in which a porous plug is embedded in the bottom of the vacuum melting furnace to strengthen stirring. However, although this method has a certain denitrification effect, the structure of the porous plug means that the blown gas cannot be spread over a wide range. Therefore, it is difficult to control and it is difficult to blow a large amount of gas into the molten metal and stir it strongly.

Therefore, sufficient denitrification effect cannot be obtained. Furthermore, it is necessary to round the plug to prevent the molten metal from being inserted into the plug, and to constantly blow gas while the molten metal is present, resulting in an enormous amount of gas consumption. Furthermore, there are drawbacks such as the carefulness of embedding the porous plug in the bottom of the furnace, and the possibility of severe melting and damage at the embedding location, which may interfere with the melting work.

The present invention has been made to solve the problems of the prior art described above, and the basic principle is that when refining molten metal in a vacuum induction melting furnace, a lance is immersed from above the molten metal and gas is blown through the lance. This is a unique feature.

FIG. 1 is an explanatory diagram showing an overview of the method of the present invention, (1)
is a vacuum chamber, (2) is an induction melting furnace, (3) is a lance, (4
) is a lance replacement device, (5) is a lance lifting device, (6)
is a pressure gauge, (7) is a flow meter, and (8) is a gas supply device.

First, the material is melted in the melting furnace (2), or molten metal is supplied from a ladle, maintained at a predetermined temperature, and the pressure inside the vacuum chamber (1) is reduced. A lance (3) for blowing gas from the top of the vacuum chamber (1) is immersed in the molten metal in the melting furnace (2), and gas is blown into the melting furnace (2) to promote stirring of the molten metal. As this blowing gas, an inert gas such as argon gas, CO gas, or a mixture thereof can be used. This gas blowing promotes denitrification.

Next, examples will be shown.

〔Example〕

Denitrification of carbon steel was carried out in a vacuum induction melting furnace under the following conditions, and the results shown in the table below were obtained. The results are graphed in Figure 2 and compared with the results when the denitrification was maintained at reduced pressure without gas injection. and show. (b) in the graph shows other results of the method of the present invention.

X Empty K 2.3”rr Blow gas amount At gas 7-5 NL/mtn-T
Amount of dissolved oN: 4 TON Temperature: 1600-1620°O As can be seen from the above results, the effect of gas injection by the immersion lance is significant, and [N]<t.

It becomes possible to produce ultra-low nitrogen steel of p-pm.

The method of the present invention is not limited to carbon steel, but can also be applied to high-alloy steels such as high Cr-containing steels with high nitrogen solubility, or alloy systems to reduce nitrogen content, and sufficient effects can be obtained.

As described above, according to the method of the present invention, it is possible to realize extremely low nitrogen content in the molten metal, and it does not have an adverse effect on large materials in the furnace body unlike the method of embedding a porous plug in the bottom of the furnace, and even during operation. It is easy to replace the lance.

Further, the depth of immersion of the lance into the molten metal and the gas flow can be set arbitrarily, which has the effect that stirring can be controlled arbitrarily.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the method of the present invention, and FIG. 2 is a graph showing changes in [N). In the figure, (1) shows a vacuum chamber, (2) shows an induction melting furnace, and (3) shows a lance. Patent applicant Nippon Kokan Co., Ltd.

Claims (1)

[Claims] When refining molten metal in a vacuum induction melting furnace,
A method for denitrifying molten metal in a vacuum induction melting furnace, characterized by immersing a lance from above the molten metal and blowing gas through the lance.